Project Summary and Relevance Project Summary: The broad, long-term objective of this collaborative project is the discovery of small molecule therapeutics that can replace antibodies as inhibitors of the PD-1 checkpoint. To date, no small molecules have been approved for this application, although the benefits of small molecules over biologicals in drug therapy is clear. This project capitalizes on the existence of a large collection (up to 30,000 samples) of structurally unique marine microbial metabolites that have shown to be a solid source for the development of anticancer agents. This collection, available at the Scripps Institution of Oceanography, UCSD, from Dr. William Fenical will be interfaced with the cancer biology lab of Dr. Yin Lu at the Nanjing University of Chinese Medicine, to screen for selective inhibitors using a commercially-available cell-based bioassay for PD-1 binding. When active metabolites are discovered, they will be screened in a variety of secondary assays to show selective binding. Finally, verified PD-1binding inhibitors will be produced in multi-milligram amounts by large-scale cultivation and provided to Dr. Lu for evaluation in mouse and rat xenograph models of select cancers. Relevance: This project aims to improve on the immunotherapy of cancer by discovering small molecules that selectively bind to the protein PD-1, which when bound to PDL-1 is responsible for the deactivation of the immune system. Replacing the current antibody (protein) therapy with a small molecule drug is likely to improve treatment efficacy and will clearly reduce drug cost.